It isn't exactly uncommon among nerdy guys who have difficulty dating in general tbh. Even non autistic guys have a harder time being single than non autistic girls.
I think it's because girls are socialized to get social support and emotional in female peers, and guys are less likely to have that with their male friends. Throw in a bunch of media bullshit where getting a girlfriend is heavily tied to success and happiness and you end up with a fixation. So the girlfriend becomes this like idealized solution for all their emotional problems - if only I had a girlfriend I'd be happy. But women are more adept finding happiness as singles. Some women fall into this trap but it seems less common in women in my experience.
It can overwhelm women they're interested in because they seem desperate and come on too strong, making it harder to get in a relationship. And really nobody can be the solution to all of someone's emotional struggles and it's unfair to expect that. But on some level guys don't know they're doing this and it ends up an unhealthy spiral of being focused on singleness making them less appealing partners, making them feel their single status more keenly. A lot of guys in that spiral (autistic or not) need to see a therapist before they'll be any good at being a partner imho.